The present invention relates to a guide-bar device for a multi-spindle lathe with a barrel comprising a plurality of guiding tubes, each of the guiding tubes supporting a bar to be machined in rotation in a fluid, the rear part of said bar being supported by a piston located in the tube.
Generally speaking and until now it was not possible to achieve, with multi-spindle lathes, speeds of rotation of the spindles as high as the speeds now achieved with the single spindle lathes of equal capacity. However, the technological evolution of the cutting tools and oils on the one hand, and the imperatives of the market on the other hand, give rise to a need to increase the speeds of rotation of the spindles of multi-spindle lathes. This is an evolution similar to the one which has taken place in the last years between the conventional single-spindle lathes with cams and the single spindle lathes with numerical control (CNC). Consequently, the technical evolution of the guide-bar devices for the multi-spindle lathes shall, in the future, play a prominent part due to the fact that the mechanical devices presently in service cannot follow the possible speeds of the spindles of multi-spindle lathes. The production capacity of multi-spindle lathes therefore depends to a large extend on improvements in guide-bar devices. The purpose of the present invention is to provide precisely such an improvement.
Known guide-bar devices comprise a barrel of steel tubes, the feed of the bar being generally provided by a feed collet located in the headstock of the lathe. Due to the low speeds of rotation, it is relatively easy to absorb the noise created by the vibrations of the rotating bars, either by providing insulating materials around the tubes of the barrel or by upholstering the whole aggregate in order to suppress the noise toward the outside. These sound dampening means however are not satisfactory because the noise is the result of vibrations and even if one could provide a perfect acoustic insulation, one would not suppress the vibrations of the bar which are transmitted along the latter in the machining area of the pieces and which cause a deterioration in the finish of the machine surface, make it difficult to machine to prescribed tolerances and accelerate the deterioration of cutting tools.
From the circular of Hermann Forch Ing., 7000 Stuttgart 80 (Vaihingen), Hauptstrasse 103, Germany, a system called PLO is known which consists of modifying existing guide-bar devices to permit the use of the cutting oil or emulsion of the machine, in order to produce a film of oil or emulsion for damping vibrations from the rotating bar. However, such a device is not satisfactory due to the fact that the rear part of the bar is not supported or centered so that the bar is floating, hammering the internal wall of its guiding tube when rotating. This produces noise and the vibrations are transmitted along the bar in the area where the pieces are machined. Further, the operator has no choice regarding the fluid to be used. He is obliged to use the same oil or cooling water in the guiding tubes which is used in the machining area of the bar. The requirements of these two uses are entirely inconsistent. Fluids which are capable of producing a hydrodynamic bearing do not have the same characteristics of viscosity, emulsion and the like as fluids (e.g. soap water) for cooling cutting tools. Moreover, the guiding tubes of the known device(s) are generally of a mechanical welded construction. The internal diameter of the tube of the barrel is selected in terms of the maximum capacity of the lathe. Thus it is not possible to choose the internal diameter according to the requirements. It is also known that for realizing a hydrodynamic support, it is necessary to adapt the internal diameter of the tubes to the diameter and the profiles of the bars to be machined and this in terms of the speeds of rotation that one wishes to achieve. Due to the fact that known devices are intended to be adapted to an already existing construction, it is often difficult or even impossible to recuperate the fluid coming from the front and rear parts of the guiding tube.
Copending U.S. patent application Ser. No. 540,383 by the same applicant describes a guide-bar device for a mutli-spindle lathe (see FIG. 1) with a hydraulic distributor for controlling the feed of a piston supporting the rear part of the bar in its guiding tube. When a new bar is to be supplied the piston is caused to retreat and it is fully received in a housing of the distributor which is then rotated in order to present an opening opposite the empty tube to be provisioned and a new bar is introduced in this tube through this opening. However, due to the fact that the tubes are mounted on a barrel which is indexed at each operation of machining while the distributor is not indexed, it is necessary to ensure that the piston is fully engaged in the guiding tube before allowing any rotating of the barrel. Such a device has the following disadvantages: The space taken up by the device is not a minimum because the piston must be fully engaged in the guiding tube in order to avoid any risk of damaging of the piston when the barrel is indexed. This requires a difficult checking to ensure that the rear part of the bar is engaged in the guiding tube at least a distance equal to the lensth of the piston. Moreover, the guiding tubes must be perfectly aligned with the housing of the piston in the distributor which itself has to be rotatively mounted.
Modern multi-spindle lathes seek to operate at the same speeds of rotation as single spindle latches with numerical control, while suppressing vibrations and noise and improving accuracy. New machines are available in which the spindles may rotate at different rates as a function of the respective cutting tools and the operations to be performed.
The object of the present invention is to realize a guide-bar device for multi-spindle latches which does not suffer from the disadvantages of the known devices, the device taking up a reduced amount of space and being designed to facilitate the automatization of new bar provisioning.